1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to an apparatus and method for driving a liquid crystal display that minimizes a gray loss of an image displayed on an RGBW-type display device.
2. Discussion of the Related Art
A variety of flat panel display devices smaller and lighter in weight than typical Cathode Ray Tube (CRT) display devices have been developed. For example, display devices such as a liquid crystal display (LCD), a Field Emission Display (FED), a Plasma Display Panel (PDP), and a Light Emitting Display (LED) have been widely used as flat panel display devices.
A typical LCD device includes a plurality of liquid crystal cells arranged in regions defined by the crossings of a plurality of data lines and a plurality of gate lines. Each liquid crystal cell includes a Thin Film Transistor (TFT) substrate and a color-filter substrate, and further includes a liquid crystal layer formed between the TFT substrate and the color-filter substrate.
The TFT substrate on which TFTs serving as switch elements are formed and the color-filter substrate on which color filters are formed are spaced apart from each other by a predetermined distance.
The LCD device generates an electric field in each pixel of a liquid crystal cell according to data signals applied to the data lines. The electric field controls the transmissivity of light through the liquid crystal layer in each liquid crystal cells to produce images. To prevent degradation that occurs to the liquid crystal device when an electric field is applied to the liquid crystal in a particular direction for too long a period, the polarity of a data signal is reversed for each frame, column, or dot.
The LCD device generates an image by mixing red, green, and blue lights provided by 3-color pixels of red (R), green (G), and blue (B). However, the light efficiency of a typical LCD device for displaying one sub-pixel using 3-color dots of red (R), green (G), and blue (B) is relatively low. More specifically, since a color filter arranged in each sub-pixel of red (R), green (G), and blue (B) allows about ⅓ of incident light to penetrate the filter, light efficiency is significantly reduced.
Korean Patent publication No. P2002-13830 (“LCD Device”) and Korean Patent publication No. P2004-83786 (“Apparatus for Driving of Display Device and Method for Driving Thereof”) disclose an RGBW type LCD device, which includes a white color filter W in additional to the red, green, and blue color filters for maintaining the color realization ratio and to improving light efficiency in an LCD device. The above-described RGBW type LCD device converts a 3-color image signal into a 4-color image signal, thereby increasing brightness of a color image.
FIG. 1 illustrates a view of a color area to be embodied in an RGBW type display device according to the related art. FIG. 1 shows Gamut plane coordinates with red (R) and green (G) axes displayed in three-dimensional orthogonal coordinates with red (R), green (G) and blue (B) axes. A square area indicated by solid lines represents colors to be displayed by a 3-color image signal, and a hexahedron area indicated by thick solid lines represents colors to be displayed by a 4-color image signal. That is, the RGBW type liquid crystal display device extends a color area in a diagonal direction as indicated by the dotted lines by adding white (W) to a 3-color of red (R), green (G), and blue (B). As a result, in a process for converting a 3-color image signal into a 4-color image signal, each coordinate in the square is extended into coordinates in the hexahedron.
In the RGBW type LCD device, an apparatus for converting a 3-color image signal into a 4-color image signal has various gain curve characteristics G1, G2, G3, and G4. Even though the gain curves G1, G2, G3, and G4 vary, brightness amplification factors in the gain curves G1, G2, G3, and G4 with respect to white (W) are the same. However, each 3-color image signal (A) with respect red (R), green (G), and blue (B) colors has a different amplification factor, such as A′, A″, and A′″. Accordingly, the brightness amplification factors of white (W) and any 3-color image signal (A) in any one of the gain curves are different from each other.
For example, when an image in which pure color with a gain value of “1” and tone color with a gain value of “2” are mixed, the brightness amplification factors are considerably different. Because the brightness amplification factors according to an inputted 3-color image signal in the RGBW type LCD device are different from each other, an image from the RGBW type LCD device is perceived differently from an image of an RGB type liquid crystal display device.
In addition, in the RGBW-type LCD device of the related art a high gain value may result in a gray overflow in some pixels resulting in color-image distortion caused by gray loss.